BURNING OF LAND. »2» 



only led to conclusions on the nature and properties of hydraulic 

 limestones, but, what is far more important, they have explained 

 the action of slacked lime upon soils, and they have thus furnish- 

 ed an invaluable means of liberating from the soil the alkalies 

 which are indispensable to the existence of plants. 



In October, the fields in Yorkshire and Lancashire have the 

 appearance of being covered with snow. The soil for miles is 

 seen covered either with lime previously slacked, or with lime 

 that has slacked itself by exposure to air. During the moist 

 months of winter, it exercises its beneficial influence on the stiff 

 clayey soils. 



According to the old theory of humus, we ought to suppose 

 that burnt lime would exercise a very injurious influence on soils, 

 by destroying the organic matter contained in them, and by thus 

 rendering them unfit to supply a new vegetation with humus. 

 But, on the contrary, it is found that lime heightens the fertility 

 of a soil. The cereals require the alkalies and silicates liberated 

 by the lime and rendered fit for assimilation by plants. If there 

 be present decaying matter yielding to the plants carbonic acid, 

 their development may be favored by this means ; but this is 

 not necessary. For if we furnish to the soil ammonia, and to 

 the cereals the phosphates essential to their growth, in the event 

 of their being deficient, we furnish all the conditions necessary 

 for a rich crop, as the atmosphere forms an inexhaustible maga- 

 zine of carbonic acid. 



In districts where fuel is cheap, an equally favorable influence 

 is exerted on clayey soils by the system of burning. 



It is not very long since that chemists observed the remarka- 

 ble changes which take place in the properties of clay when it is 

 burned : these were first studied in the analysis of several sili- 

 cates of alumina. Many of them, which are not at all attacked 

 by acids in their natural state, acquire complete solubility when 

 they are previously melted by heat. To this class of silicates 

 belong pipe and potter's clay, loam, and the different varieties of 

 clay occurring in soils. In the natural state of clay, it may be 

 digested with concentrated sulphuric acid for hours, without dis- 

 solving in any appreciable quantity ; but when the clay is slightly 

 burnt (as is done, for example, in several alum works) it dissolves 

 7* 



